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| United States Patent |
5,053,808
|
|
Takagi
|
October 1, 1991
|
Image forming apparatus
Abstract
The improved image forming apparatus with a capability for automatically
identifying the type of originals measures the reflected light from an
original of interest with at least two sensors for the light of at least
one of three primary colors, constructs a discriminant function that makes
use of the differences in spectral reflection density between originals
and which uses as parameters all the values of measurements obtained or
with the higher and lower values being cut off, and automatically
identifies the type of the original by discriminating color photographic
originals from another type of originals such as color printed originals
or black-and-white originals on the basis of the value of said
discriminant function. The image forming apparatus may measure the
reflected light from the original with sensors for the light of three
primary colors and identify a low-density, low-constant original by means
of a predetermined discriminant formula. Based on the results of such
identification, the image forming apparatus selects the proper
light-sensitive materials and exposure conditions according to the type of
original of interest or the low-density, low-constant to original to be
used and performs appropriate image formation.
In spite of the use of a simple discriminant function or formula, the image
forming apparatus is capable of correct identification of the type of
original whether its size is regular or irregular as in the case of
small-size documents or bulky materials, thereby allowing for appropriate
image formation.
| Inventors:
|
Takagi; Atsushi (Ashigara, JP)
|
| Assignee:
|
Fuji Photo Film Co., Ltd. (Kanagawa, JP)
|
| Appl. No.:
|
413557 |
| Filed:
|
September 27, 1989 |
| Current U.S. Class: |
355/38; 355/68; 355/77; 399/178 |
| Intern'l Class: |
G03B 027/73 |
| Field of Search: |
355/38,68,69,214,311,326,327
356/444,404
|
References Cited
U.S. Patent Documents
| 3796060 | Jan., 1989 | Mizude | 355/214.
|
| 4731671 | Mar., 1988 | Alkofer | 355/38.
|
| 4745465 | May., 1988 | Kwon | 355/38.
|
| 4829371 | May., 1989 | Hiramatsu et al. | 355/38.
|
| 4830501 | May., 1989 | Terashita | 356/404.
|
| 4860059 | Aug., 1990 | Terashita | 355/38.
|
| Foreign Patent Documents |
| 63-232681 | Sep., 1988 | JP.
| |
Primary Examiner: Hix; L. T.
Assistant Examiner: Rutledge; D.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
What is claimed is:
1. An image forming apparatus comprising:
at least two sensors for the light of each of at least one of three primary
colors for measuring the reflected light from an original, said sensors
having sensitivity peaks at different wavelengths within the wavelength
region of the light of said at least one primary color,
means for identifying the type of said original by the values of
measurements with said sensors, and
means for forming an image in accordance with the so identified type of
original, identification of said original being performed in such a way
that color photographic originals are distinguished from color printed
originals and black-and-white originals based on the value of a single
discriminant function that uses said plural values of measurements as
parameters for said discriminant function.
2. An image forming apparatus according to claim 1 wherein said original is
a color original.
3. An image forming apparatus according to claim 1 wherein said three
primary colors are red, green and blue.
4. An image forming apparatus according to claim 1 wherein a total of six
sensors are used, two being dedicated to each of the three primary colors.
5. An image forming apparatus according to claim 4 wherein said six sensors
consist of two sensors having sensitivity peaks at 400.+-.30 nm and
450.+-.30 nm within the wavelength region of the blue light, two sensors
having sensitivity peaks at 540.+-.15 nm and 570.+-.15 nm within the
wavelength region of the green light, and two sensors having sensitivity
peaks at 630.+-.40 nm and 700.+-.40 nm within the wavelength region of the
red light.
6. An image forming apparatus according to claim 1 wherein said
discriminant function is a linear discriminant function.
7. An image forming apparatus according to claim 1 wherein said
discriminant function is of the second order.
8. An image forming apparatus comprising:
means for measuring the reflected light from a predetermined region of
photometry including an original;
means for distinguishing color photographic originals from color printed
originals and black-and-white originals on the basis of the obtained
values of photometric measurements,
means for correcting image forming conditions of said apparatus based on
the size and the type of original by performing mathematical operations
only on photometric values from which photometric values below a
predetermined low level and/or those values exceeding a predetermined high
level have been excluded, and
means for forming an image in accordance with the identified type of
original.
9. An image forming apparatus according to claim 8 wherein said means for
measuring comprises a platen glass on which the original is disposed and
said region of photometry is the range over which the platen glass
carrying the original is prescanned.
10. An image forming apparatus according to claim 8 wherein said original
is a color original.
11. An image forming apparatus according to claim 8 wherein said values of
photometric measurements are obtained by using, for the light of each of
at least one of the three primary colors, at least two sensors having
sensitivity peaks at different wavelength within the wavelength region of
the light of one primary color.
12. An image forming apparatus according to claim 8 wherein said three
primary colors are red, green and blue.
13. An image forming apparatus according to claim 11 wherein said values of
photometric measurements are obtained with a total of six sensors, two of
which are dedicated to each of the three primary colors.
14. An image forming apparatus according to claim 13 wherein said six
sensors consist of two sensors having sensitivity peaks at 400.+-.30 nm
and 450.+-.30 nm within the wavelength region of the blue light, two
sensors having sensitivity peaks at 540.+-.15 nm and 570.+-.15 nm within
the wavelength region of the green light, and two sensors having
sensitivity peaks at 630.+-.40 nm and 700.+-.40 nm within the wavelength
region of the red light.
15. An image forming apparatus according to claims 8 wherein said
mathematical operations for identifying the type of original are performed
to calculate the value of a discriminant function which uses said values
of photometric measurements as parameters.
16. An image forming apparatus according to claim 15 wherein said
discriminant function is a linear discriminant function.
17. An image forming apparatus according to claims 15 wherein said
discriminant function is of the second order.
18. An image forming apparatus which applies light beams to the image of a
color original, with the reflected light being used to form a color image
on a light-sensitive material by imagewise exposure, which image is then
rendered visible as a reproduced color image, the improvement comprising:
means for reading information from the image of the color original and
obtaining a color density distribution of the original image for the light
of each of three primary colors,
means for identifying a low-density, low-contrast original by means of
discriminant formulas containing a plurality of parameters obtained from
said color density distributions, comprising image area density,
background density and the proportion of the background area, and
means for performing a predetermined density correction for the so
identified low-density, low-contrast original.
19. An image forming apparatus according to claim 18 wherein said three
primary colors are red, green and blue.
20. An image forming apparatus according to claim 18 wherein photometry is
performed at a predetermined number of measuring locations at give
intervals in the scanning direction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus. More
particularly, the present invention relates to an image forming apparatus
that is capable of accurately distinguishing color photographic originals
at least from color printed originals or black-and-white originals and
which forms image according to the so distinguished type of original. The
present invention also relates to an image forming apparatus capable of
achieving faithful color density reproduction even from low-density, in
particular, low-density low-contrast originals.
2. Prior Art
Image forming apparatus including various copiers capable of duplicating
color originals, as well as color image printers are gaining increasing
popularity these days.
In order to produce satisfactory color image with these color image forming
apparatus, good balance must be attained not only in colors but also in
densities.
With most of these image forming apparatus, in particular, color copiers,
photographs and printed matter are used as color originals. However,
different colorants are used in photographs and printed matter. Further,
they have different spectral luminous efficiencies and require the use of
copying materials having different spectral sensitivities. On account of
these differences, the images of copies from photographic originals have
had a different color balance than those from printed originals if they
are duplicated under the same copying conditions. For example, color
printed originals have a great overlap between the spectral density
distributions of magenta and cyan inks. Thus, color printed originals have
a high magenta density and color copiers that are adjusted to produce good
copies of color printed originals are to be operated under copying
conditions that provide suppressed magenta density. Therefore, if color
photographic originals are duplicated under such image forming conditions,
the production of magenta color is so limited as to form color copied
images of green shades.
Color printed originals and color photographic originals also differ in the
gradation of their image, so that if color photographic originals are
duplicated on contrasty light-sensitive materials (i.e., those which are
optimal for duplicating color printed originals) with copiers that employ
silver halide photographic materials and various other light-sensitive
materials, medium tone will not be effectively reproduced and only hard
images will result. Therefore, in order to obtain an image of good quality
with a single unit of image forming apparatus according to various types
of color originals, it is necessary to identify the type of original to be
duplicated and to select the proper image forming conditions (e.g. the
amount by which color filters are adjusted and the amount of exposure) and
the right kind of light-sensitive material according to the type of said
original. However, this problem has not been fully considered in the
design of prior art image forming apparatuses and if image forming
conditions and light-sensitive materials are not changed in a single unit
of image forming apparatus according to the type of original, it is
impossible to obtain satisfactory image from either color printed
originals or color photographic originals.
An image forming apparatus has also been proposed that enables the operator
to manipulate selection keys according to such criteria as the presence or
absence of halftone dots, thereby selecting appropriate image forming
conditions that are optimal for the particular type of color original.
However, the recent advances in color printing technology are so great
that it is considerably difficult for unskilled operators to make accurate
identification as to whether the original of interest is a color picture
of the color printed matter obtained from color pictures. Further, the
image forming process by operators is far from being efficient.
There have also been proposed several methods for identifying various types
of color originals by means of image readers, as well as image forming
apparatus that have such identifying means. However, in most identifying
methods proposed so far, a plurality of functions involving measured
values obtained from the image reader must be used in combination in order
to identify the specific type of a color original of interest. In addition
to this problem of complexity and difficulty in control, a further
improvement is required of the precision that can be attained in the
results of identification.
Prior art image forming apparatuses that are intended to duplicate color
originals have various kinds of light-sensitive materials in stock that
are optimal for the specific types of color originals to be duplicated but
they are not usually furnished with light-sensitive materials dedicated to
black-and-white originals and instead they form black-and-white image on
color light-sensitive materials. Thus, standard exposure conditions that
are optimal for black-and-white originals such as black-and-white
photographs and printed matter have not been fully taken into account in
the design of image forming apparatus of the type described above. As a
result, if a black-and-white original is duplicated on a low-contrast,
light-sensitive material that is optimal for duplicating color
photographic originals (which is hereunder referred to as a "soft
light-sensitive material"), the copied image will have a red shade as in
the case where color printed originals are duplicated on soft
light-sensitive materials and no satisfactory black-and-white copied image
can be obtained. This is true whether the black-and-white original is a
photograph or printed matter. It has therefore been desired to develop an
apparatus that is capable of distinguishing color photographic originals
not only from color printed originals but also from black-and-white
originals.
In prior art image forming apparatus, the photometric region of the same
length as, for example, the size of the light-sensitive material on which
image is to be formed is often scanned either during prescanning or before
reading the necessary information from the original of interest. All the
data thus read are used to perform mathematical operations, thereby
identifying the type of original to be duplicated. If, under these
circumstances, the size of document to be copied is smaller than a
predetermined area of the platen glass or the area of photometric region
which is equal to the light-sensitive material of interest as in the case
of copying color documents of small size, in particular, making enlarged
copies of color prints of size E (82 mm.times.116 mm) or copying color
documents of irregular sizes, or if the document is not properly placed on
the platen glass, the document illuminating light that passes through the
platen glass on a position way off the document during photometric
scanning of the document surface is sometimes reflected by the white
underside of the top cover to be directly launched into sensors. As a
result, even the white area of the top cover is read as part of the image
of document and subjected to mathematical operations. This can cause
failure to correctly identify the document type and the color photographic
original is detected either as a color printed original or as an
intermediate original containing both color photographic and printed
images.
A need sometimes arises to copy a bulky material such as a package or
commercial goods with the top cover left open or to copy a certain page or
pages of a thick book placed face down on the platen glass, again with the
top cover left open. In these cases as well the case where the color
document to be copied is smaller than the light-sensitive material on
which image is to be formed, the following big problems will inevitably
occur. If the document to be copied has a smaller image forming area than
the photometric region or is a thick book that forms a large hollow
portion around it or along the center margin which should inherently
belong to the document region, the document illuminating light will pass
unimpeded through the photometric region where no document is present or
through the area of the platen glass corresponding to said hollow portion.
If this occurs in the copying process, an area that hardly produces
reflected light will occur in part of the document region which is
inherently supposed to receive some reflected light. In other words, the
occurrence of this phenomenon allows sensors to read such defective region
as one of very high density and if mathematical operations for
identification are performed on the basis of the resulting data, one often
fails to identify the correct document type.
Some versions of the prior art image forming apparatus are capable of
selecting an optimum light-sensitive material and setting optimum standard
exposure conditions according to the document type identified by the
conventional methods described above, and then performing exposure under
said standard conditions to form image. With such color image forming
apparatus, in particular, color copiers, color image forming conditions
are initially set at the time of system installation or thereafter
adjusted periodically so as to insure the formation of reproduced image
having colors and densities faithful to the image of color original. With
silver halide color image forming apparatus, photographic documents which
require faithful reproduction of medium tone are copied on soft (low
contrast) light-sensitive materials having comparatively low
gamma-characteristics whereas printed documents which also require good
contrast are copied on normal (contrasty) light-sensitive materials having
comparatively high gamma-characteristics. In addition, the color image
forming conditions are varied in such a way as to optimize the densities
and color reproduction that are required for ideal image reproduction.
Color reflection type originals generally have a gamut of various densities
and colors, so the average density of either the whole document or the
image areas of the document is detected from the image of document and
correction is made in such a way as to provide satisfactory color
reproduction for the detected average density. If, in the case where image
is to be formed on a light-sensitive material having the characteristics
shown by curve a in FIG. 15, the overall density (e.g. average density) Do
of a color printed original is found to be equal to Dc, the overall color
density Dp of a reproduced image is equal to Da. Since Da>Dc, in order to
provide satisfactory color density reproduction, the characteristic curve
a of the light-sensitive material is laterally shifted until Dp becomes
equal to Dc. In other words, density correction is effected in such a way
that when the density of original image Do is Dc, the density of
reproduced image Dp is equal to Db (=Dc).
On the other hand, most black-and-white copiers are so designed that
background areas of light colors and the nearly white background are
rendered white by eliminating the light colors through proper density
correction typically exemplified by an increase in the quantity of light.
Most frequently used color reflection type originals are such that many of
the image areas present have densities equal to the average density but
even documents having an overall dark density sometimes contain characters
of lighter density or areas of medium density. If such documents are read
for density correction, not only the dark areas but also the areas of
light and medium density are scanned simultaneously and the document of
interest is judged to be a dark document. Accordingly, density control is
effected in such a way as to reproduce a darker image on the dark
document. A problem with this approach of control for density correction
is that although colors of high density are reproduced satisfactorily,
colors in the low-density areas are skipped.
Conversely, if documents that have a low average density but which exhibit
high contrast between a wide area of the white background and characters
are corrected to produce a darker density by reducing the amount of light,
fogging occurs in the white background which hence does not become
snow-white.
Normal contrasty light-sensitive materials usually have comparatively high
gamma-values and their characteristic curve has a large gradient that
departs from the straight line of .gamma.=1 in FIG. 15. Reproduction with
such materials is poor in the low-density areas. To cope with this
problem, documents having an overall low density may be controlled in such
a way that the quantity of light is not reduced to effect compensation for
color densities. However, with documents such as maps that have an overall
low density but which have background areas of relatively high density and
light colors, if density correction is performed in such a way as to
eliminate the color of background areas by increasing the quantity of
light (i.e., the type of correction method employed with black-and-white
copiers) or if the amount of light is not sufficiently reduced to effect
compensation for color densities, the background areas will not assume a
full color and will instead remain white, with consequent formation of an
image that poorly reproduces colors in the low-density areas. With
contrasty normal light-sensitive materials, satisfactory color
reproduction is possible if the original is printed matter but no
satisfactory colors can be produced in the low-density areas.
Thus, prior art image forming apparatuses which are incapable of
distinguishing low-density originals with a wide area of the white
background from low-density, low-contrast originals such as maps having
background areas of high relatively density and light colors have failed
to automatically produce images with efficient reproduction of color
densities from either type of originals.
SUMMARY OF THE INVENTION
The first and principal object, therefore, of the present invention is to
solve the aforementioned problems of the prior art by providing an image
forming apparatus that accurately distinguishes, by a simple method, color
photographs at least from color printed matter when the document is a
color original, or distinguishes black-and-white originals at least from
color photographs and which hence is capable of forming image under
optimal conditions according to the identified type of original.
A second object of the present invention is to provide an image forming
apparatus of a type that performs prescanning over a length corresponding
to the size of light-sensitive material used and which is capable of
accurately distinguishing color photographic originals at least from color
printed originals or black-and-white originals, thereby forming
appropriate image according to the detected type of original even if the
document to be copied is smaller than the range of photometry by
prescanning (e.g. in the case where enlarged copies of small-size
documents, say, prints of size E are made or where documents of irregular
sizes are copied) or even if thick books, packages and other bulky
materials are copied with the top cover of the copier being left open.
A third object of the present invention is to provide an image forming
apparatus which automatically makes distinction between low-density
originals with a wide area of the white background and low-density,
low-contrast originals with background areas of relatively high density on
the basis of color density distributions obtained from information read
from the image of original and which is capable of compensating for color
densities in such a way as to provide an optimum quantity of light for
each of the documents to be processed.
The present inventors conducted various studies in order to attain the
three objects described above and found the following: 1) the spectral
reflection density of a color photographic image represented by curve 2 in
FIG. 1 has a distinguishable difference from the spectral reflection
density of a color printed image represented by curve 3; 2) the spectral
reflection density of a black-and-white image represented by curve 4 is
similar to the spectral reflection density of a color printed image but is
different from the spectral reflection density of a color photographic
image whether the black-and-white image is a photographic or printed
image; 3) therefore, at least a black-and-white image or a color printed
image can be precisely distinguished from a color photographic image by
means of a discriminant function; 4) an appropriate image can be obtained
by effecting image formation according to the type of original identified
by the discriminant function; and 5) appropriate black-and-white image
with no color shade could be obtained when image formation was effected
using a light-sensitive material and standard exposure conditions that
were optimal for the reproduction of color printed image. The present
invention has been accomplished on the basis of these findings.
According to its first aspect, the present invention provides an image
forming apparatus having at least two sensors for the light of at least
one of three primary colors for measuring the reflected light from an
original, said sensors having sensitivity peaks at different wavelengths
within the wavelength region of the light of said at least one primary
color, the type of said original being identified by the values of
measurements with said sensors, and image being formed in accordance with
the so identified type of original. Identification of said original is
performed in such a way that at least color photographic originals are
distinguished from another type of originals by the value of a
discriminant function that uses said plural values of measurements as
parameters.
According to its second aspect, the present invention provides an image
forming apparatus which measures the reflected light from a predetermined
region of photometry including an original and which distinguishes at
least color photographic originals from another type of originals on the
basis of the obtained values of photometric measurements, with image being
formed in accordance with the identified type of original. Mathematical
operations for identifying the type of original are performed with
photometric values below a predetermined low level and/or those values
exceeding a predetermined high level being excluded from said values of
photometric measurements.
In a preferred embodiment of each aspect, said another type of originals is
a color printed original or a black-and-white original.
In another preferred embodiment of each aspect, said original is a color
original and said another type of originals is a color printed original.
In still another preferred embodiment of the first aspect, a total of six
sensors are used, two being dedicated to each of the three primary colors.
In still another preferred embodiment of the second aspect, said region of
photometry is the range over which the platen glass carrying the original
is prescanned.
In a further preferred embodiment of the second aspect, said values of
photometric measurements are obtained by using, for the light of at least
one of the three primary colors, at least two sensors having sensitivity
peaks at different wavelengths within the wavelength region of the light
of one primary color.
In yet another preferred embodiment of the second aspect, said values of
photometric measurements are obtained with a total of six sensors, two of
which are dedicated to each of the three primary colors.
In a further preferred embodiment of each aspect, the six sensors consist
of two sensors having sensitivity peaks at 400.+-.30 nm and 450.+-.30 nm
within the wavelength region of the blue light, two sensors having
sensitivity peaks at 540.+-.15 nm and 570.+-.15 nm within the wavelength
region of the green light, and two sensors having sensitivity peaks at
630.+-.40 nm and 700.+-.40 nm within the wavelength region of the red
light.
In another preferred embodiment of each aspect, said discriminant function
is a linear discriminant function.
In still another preferred embodiment of each aspect, said discriminant
function is of the second order.
According to its third aspect, the present invention provides an image
forming apparatus which applies light beams to the image of a color
original, with the reflected light being used to form a color image on a
light-sensitive material by imagewise exposure, which image is then
rendered visible as a reproduced color image. In this apparatus,
information is read from the image of the color original to obtain a color
density distribution of the original image for the light of each of three
primary colors, and a low-density, low-contrast original is identified by
means of discriminant formulas containing three parameters obtained from
said color density distributions, i.e., image area density, background
density and the proportion of the background area, with a predetermined
density correction being performed for the so identified low-density,
low-contrast original.
In a preferred embodiment of each of the first, second and third aspects,
said three primary colors are red, green and blue.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the spectral reflection density distributions of
a color photographic image, a color printed image and a black-and-white
image;
FIG. 2 is a graph showing the sensitivity characteristics of sensors that
are applicable to the image forming apparatus of the present invention;
FIG. 3 is a schematic sketch of a typical image sensor assembly that may be
used in the practice of the present invention;
FIG. 4 is a diagrammatic representation of a silver halide photographic
copier in which the image forming apparatus of the present invention is
used;
FIG. 5 is a block diagram showing one construction of the document (or
original) identifying unit of the silver halide photographic copier shown
in FIG. 4;
FIG. 6 is a block diagram showing another construction of the document (or
original) identifying unit of the silver halide photographic copier shown
in FIG. 4;
FIG. 7 is a block diagram showing one construction of the exposure control
unit of an image forming apparatus of the present invention;
FIG. 8 is a histogram of the densities obtained by performing photometric
measurements on a color original smaller than the region of photometry in
an image forming apparatus according to the second aspect of the present
invention;
FIG. 9 is a histogram of the densities obtained by performing photometric
measurements on a color original in the image forming apparatus of the
present invention, which original produces either hollow portions in the
region of photometry or non-document areas;
FIG. 10 is a graph showing the results of identifying the type of color
originals with the image forming apparatus of the present invention;
FIG. 11 is a schematic cross section of the essential part of an image
forming apparatus according to the third aspect of the present invention;
FIG. 12 is a front view of the sensor assembly used in the image forming
apparatus shown in FIG. 11;
FIG. 13 is a graph showing the envelope of the histogram of document
density distribution constructed with the image forming apparatus of the
present invention;
FIG. 14 is a block diagram showing the control unit of the image forming
apparatus of the present invention; and
FIG. 15 is a graph showing the procedure of density correction performed in
a prior art image forming apparatus.
DETAILED DESCRIPTION OF THE INVENTION
The image forming apparatus of the present invention is described below in
greater detail with reference to the preferred embodiments shown in the
accompanying drawings.
The description starts with the first aspect of the present invention shown
in FIGS. 1-6. According to this first aspect, at least two types of
originals can be distinguished from each other by the following method.
The reflected light from an original in the image forming apparatus of the
present invention is measured with at least two sensors for the light of
each of three primary colors, for example, red (hereinafter abbreviated as
R), green (G) and blue (B), or for the light of at least one primary
color, the sensors have sensitivity peaks at different wavelengths within
the wavelength regions of the light of three primary colors or within the
wavelength region of said at least one primary color. The type of the
original is identified by distinguishing at least color photographic
originals from another type of originals such as color printed originals
or black-and-white originals using as the criterion the value of a
discriminant function that uses said plural, say, six, values of
measurements as parameters.
As mentioned above, the image forming apparatus of the present invention
uses the value of a discriminant function, preferably a linear
discriminant function, as the criterion for determining whether the
original from which a black-and-white or color image is to be formed is a
color photograph or color printed matter or a black-and-white original.
A linear discriminant function may be defined as follows: When a plurality
of samples within each of groups A and B have "p" characteristic values x,
a composite variable Z is constructed by the linear combination
Z=a.sub.1 x.sub.1 +a.sub.2 x.sub.2. . . +a.sub.i x.sub.i . . . +a.sub.p
x.sub.p (i=1, 2, . . . ,p) which is used as the discrimination rule, and
according to the magnitude of this composite variable Z, decision is made
as to whether a sample of interest belongs to group A or B. Coefficients
a.sub.1, a.sub.2, . . . , and a.sub.p are determined so as to insure
reliable identification of group A or B from a given set of data, namely,
to insure that S.sub.B /S.sub.W, the ratio of S.sub.B which is the
variation between groups A and B (inter-class variation) to S.sub.W which
is the variation in each group (intraclass variation), will assume the
highest value.
While the discriminant function Z=f(x.sub.1, . . . , x.sub.n) used in the
present invention is preferably a linear one as described above, precise
separation may sometimes be accomplished by using a second-order
discriminant function if the degree of scattering of values in each group
to be discriminated differs greatly from group to group. Here, the
second-order discriminant function is generally given by the following
equation:
##EQU1##
In addition to the linear discriminant function and second-order
discriminant function described above, discriminant functions of the third
order and higher, as well as other special discriminant functions may be
used as the discriminant function Z=f(x.sub.1, . . . , x.sub.n) in the
present invention. However, discriminant functions of lower orders,
especially a linear discriminant function, are preferred since the higher
the order, the greater the number of terms that are involved in
mathematical operations and also special discriminant functions require
complicated procedures in mathematical operations.
We now describe the image forming apparatus of the present invention with
particular reference to the following case: the reflected light from an
original is measured with two sensors for the light of each of three
primary colors which have sensitivity peaks at different wavelengths
within the wavelength ranges of the light of the three primary colors; a
discriminant function, in particular a linear discriminant function, is
constructed that uses the resultant six values of measurements as
parameters; the type of the original is identified by distinguishing at
least color photographic originals from color printed originals or
black-and-white originals using the value of said discriminant function as
the criterion.
FIG. 1 shows the spectral reflection density distributions of a color
photographic image, a color printed image and a black-and-white image
which have typical color distributions. The spectral reflection density
distribution of a color photographic image is represented by the solid
line 2, that of a color printed image by the dashed line 3, and that of a
black-and-white image by the one-long-and-one-short dashed line 4.
As is clear from FIG. 1, the color photographic image has higher densities
than the other images at wavelengths in the neighborhood of 400 and 450
nm. The magenta dye used in the color photographic image has a maximum
density (maximum absorption wavelength) in the neighborhood of 530-560 nm
whereas the cyan dye has a maximum density at about 630 nm. The cyan and
magenta dyes have lower densities on either side of their respective
maximum absorption wavelengths. The magenta ink used in the color printed
image has a maximum density at about 570 nm whereas the cyan ink has a
substantially constant density level in the neighborhood of 600-680 nm. At
wavelengths longer than 700 nm, the color printed image decreases in
density more sharply than the color photographic image and the
black-and-white image. In contrast, the black-and-white, whether it is a
photographic image or a printed image, has a substantially constant
density level in each of the yellow (400-450 nm), magenta (530-580 nm) and
cyan (600-700 nm) ranges.
Thus, the color photographic image, color printed image and black-and-white
image have different density distributions in each of the wavelength
ranges of the light of three primary colors. Stated more accurately, there
is some similarity between the density distributions of the color printed
image and black-and-white image and these images can be clearly
distinguished from the color photographic image in the wavelength ranges
of the light of three primary colors. It is therefore concluded that the
type of an original of interest from which an image is to be formed can be
identified in an easy and precise manner by the following method: a number
of color photographic originals, color printed originals and
black-and-white originals are illuminated under a certain light source and
the resulting reflected light is subjected to photometric measurements of
reflection or absorption density with six sensors having sensitivity peaks
around those wavelengths in the respective wavelength ranges of the light
of three primary colors where maximum densities characteristic of both
color printed originals and color photographic originals occur
(illustrative sensitivity characteristics of these sensors are shown in
FIG. 2); on the basis of the measured data, a linear discriminant function
for identifying the types of originals which uses the values of
measurements as parameters is constructed according to the already
described discrimination rule (i.e., a linear discriminant function for
determining the value of composite variable Z), and the value of this
function is used as the criterion for identifying the type of originals.
Based on this conclusion, the present inventor fabricated an image sensor
assembly of the type shown in FIG. 3 and generally indicated by 150. This
sensor composed of a total of six sensors having the sensitivity
characteristics shown in FIG. 1 and these six sensors were:
sensors 150b.sub.1 and 150b.sub.2 having sensitivity peaks 400 .+-.30 nm
and 450.+-.30 nm within the wavelength range of the blue (B) light;
sensors 150g.sub.1 and 150g.sub.2 having sensitivity peaks at 540 .+-.15 nm
and 570.+-.15 nm within the wavelength range of the green (G) light; and
sensors 150r.sub.1 and 150r.sub.2 having sensitivity peaks at 630 .+-.40 nm
and 700.+-.40 nm within the wavelength range of the red (R) light.
Using this image sensor 150, the present inventor measured reflection
density for about 300 samples each of color photographic originals and
color printed originals of size A4. With r1, g1 and b2 (the output values
of sensors 150r.sub.1, 150g.sub.1 and 150b.sub.2, respectively) as well as
r1-r2 (the difference between the outputs of sensors 150r2 and 150r1),
g2-g1 (the difference between the outputs of sensors 150g.sub.2 and
150g.sub.1) and b2-b1 (the difference between the outputs of sensors
150b.sub.2 and 150b.sub.1) being taken as parameters, the linear
discriminant function shown below (Discriminant Function 1) was
constructed in accordance with the discrimination rule already described
above.
In the experiment, a halogen lamp with ratings of 80 V and 150 W was used
as a light source. In the measurements with the sensors, the reflected
light from each original was shaped to a slit of the size 10 mm.times.100
mm and the average of 70 values of reflection density measured at
intervals of 3 mm along the 210-mm side of A4 size sheet was taken.
DISCRIMINANT FUNCTION 1
Z=a.sub.1 +a.sub.2 *r1+a.sub.3 *g1+a.sub.4 *b2+a.sub.5 *R+a.sub.6
*G+a.sub.7 *B
If Z<0 in this Discriminant Function 1, the color original of interest is
judged to be printed matter and if Z.gtoreq.0, it is judged as a
photograph.
Coefficients a.sub.1 -a.sub.7 were so determined that the ratio of S.sub.B
to S.sub.W for the printed and photographic originals would assume the
greatest value and they were:
a.sub.1 =-14.33
a.sub.2 =-0.11
a.sub.3 =-0.37
a.sub.4 =0.45
a.sub.5 =1.19
a.sub.6 =-0.67
a.sub.7 =-0.96
Symbols R, G and B in Discriminant Function 1 denote r1-r2, g2-g1 and
b2-b1, respectively.
The present inventor conducted another experiment on 30 samples each of
color printed and photographic originals and 16 samples of black-and-white
originals using the image sensor assembly 150 and the light source which
were the same as those employed in constructing Discriminant Function 1.
Reflection densities were measured at the specified wavelengths under the
same conditions as described above and based on the data of these
measurements, Z was calculated by Discriminant Function 1 to classify the
originals according to their type. The results are shown in Table 1 below,
in which sample Nos. 1-30 were color printed originals, sample Nos. 31-60
were color photographic originals, and sample Nos. 61-76 were
black-and-white originals, of which Nos. 61-63 were photographs and Nos.
64-76 were printed matter.
TABLE 1-1
______________________________________
sample No.
r1 g1 b2 R G B Z
______________________________________
1 36 44 48 3 7 2 -16.01
2 48 47 55 3 10 -2 -13.46
3 49 75 78 2 0 10 -19.59
4 75 101 118 4 7 16 -22.14
5 40 45 52 3 6 3 -15.31
6 54 56 65 4 5 2 -12.25
7 51 53 50 3 9 -5 -14.71
8 84 73 115 4 20 18 -24.75
9 74 81 106 3 12 13 -21.69
10 32 43 46 2 5 0 -14.03
11 50 113 113 4 -7 22 -22.46
12 50 61 52 3 9 -5 -17.54
13 69 72 73 4 17 0 -22.34
14 50 38 25 4 14 -17 -10.94
15 32 88 91 4 -7 21 -20.19
16 41 46 46 4 5 -1 -12.79
17 100 98 50 6 15 -28 -15.12
18 87 114 118 5 -1 13 -18.84
19 49 67 71 2 3 0 -12.19
20 66 61 39 3 14 -13 -19.94
21 49 49 52 2 8 -1 -16.10
22 30 53 59 3 1 7 -14.51
23 12 20 24 3 0 0 -11.64
24 49 52 49 3 3 -6 -9.59
25 25 48 52 2 2 8 -18.08
26 21 25 35 2 3 1 -10.73
27 35 44 65 3 4 9 -12.96
28 21 26 38 2 -1 5 -10.91
29 26 36 33 3 4 -2 -12.85
30 27 28 34 3 6 -1 -11.85
______________________________________
TABLE 1-2
______________________________________
sample No.
r1 g1 b2 R G B Z
______________________________________
31 54 58 60 10 -4 -14 13.29
32 25 31 26 9 -3 -20 15.07
33 39 47 43 11 -5 -14 13.22
34 57 55 53 11 -1 -26 21.62
35 63 64 60 16 -3 -17 19.43
36 48 52 48 11 -4 -23 20.60
37 53 51 49 13 -1 -27 25.08
38 66 66 59 13 -3 -28 24.90
39 49 48 47 11 -2 -27 24.02
40 69 77 68 17 -7 -22 26.23
41 66 86 82 16 -16 -7 19.97
42 26 27 26 6 0 -13 4.14
43 68 71 66 16 -4 -23 25.42
44 67 61 49 18 0 -29 27.04
45 74 88 101 19 -11 6 14.64
46 24 25 23 6 -1 -17 8.26
47 31 32 33 7 -1 -14 7.71
48 68 92 99 15 -15 3 13.72
49 48 43 41 20 1 -16 21.42
50 41 44 41 11 -3 -24 22.91
51 124 107 109 24 -2 -12 22.91
52 26 24 23 7 1 -21 12.10
53 39 39 45 8 -3 -6 4.49
54 66 77 76 17 -11 -11 22.28
55 24 23 23 6 0 -19 10.25
56 23 23 22 5 0 -19 8.72
57 53 51 55 26 1 1 15.03
58 29 33 33 6 -1 -10 2.53
59 30 32 33 6 -1 -10 1.83
60 54 69 72 12 -9 -6 12.67
______________________________________
TABLE 1-3
______________________________________
sample No.
r1 g1 b2 R G B Z
______________________________________
61 77 81 81 -1 -2 -4 -12.33
62 29 30 28 0 1 -9 -8.05
63 63 64 64 1 0 -4 -11.11
64 42 42 41 1 0 -3 -11.97
65 49 49 47 1 0 -3 -12.63
66 33 34 33 1 0 -3 -11.62
67 31 32 37 4 1 0 -8.84
68 11 14 15 2 -2 2 -12.17
69 31 29 32 3 2 1 -12.80
70 66 67 69 7 0 2 -8.92
71 8 8 11 2 1 1 -12.47
72 13 12 16 3 1 -2 -8.18
73 6 6 8 2 2 -3 -9.69
74 10 10 13 4 1 0 -9.19
75 46 48 53 5 0 0 -7.35
76 85 86 88 6 2 2 -12.02
______________________________________
If Z<0 in Discriminant Function 1, the original of interest is judged to be
either a color printed original or a black-and-white original and if
Z.gtoreq.0, it is judged as a color photographic original.
Thus, the data in Table 1 shows the following: if the light of each of
three primary colors is measured with two sensors having sensitivity peaks
at different wavelengths within the associated wavelength range and if the
resulting six values of measurements are used as parameters, color
photographic originals can be effectively differentiated from color
printed originals or black-and-white originals by a single discriminant
function unlike in the case of the prior art methods which require at
least two discriminant functions to be used in combination.
The values that can be used as parameters in the discriminant function for
effective operation of the image forming apparatus of the present
invention are by no means limited to those described above (r1, g1, b2,
r1-r2, g2-g1, and b2-b1) and various other values may be employed, such as
the six output values of the sensors and the sum, rather than the
difference, of the values of measurements within the wavelength range of
the light of each of three primary colors. However, in order to insure
that color photographic originals are precisely differentiated from
black-and-white originals or color printed originals by a simple
discriminant function, at least one value of measurement within the
wavelength range of the light of each of three primary colors and the
difference between the values of measurements within said wavelength are
preferably used as parameters as in the case of Discriminant Function 1.
FIG. 4 is a diagrammatic representation of a silver halide photographic
copier in which the image forming apparatus of the present invention is
used. The silver halide photographic copier generally indicated by 10 in
FIG. 4 (which is hereinafter referred to simply as copier 10) comprises
three basic units 16, 18 and 20. The unit 16 is on the right side and
light-sensitive materials are supplied therefrom; the unit 18 in the upper
part of the copier 10 is an exposing unit, and the unit 20 in the lower
part is a processing unit.
The exposing unit 18 has disposed therein an image sensor assembly 150 of
the same type as shown in FIG. 3 and used in constructing Discriminant
Function 1 and an original identifying section 152 which, on the basis of
the values of measurements with the image sensor assembly 150, determines
whether the original of interest is a color photograph, color printed
matter or a black-and-white original by Discriminant Function 1 and which
then supplies the resulting discrimination signal to a lens unit 92, or,
if the copier has a capability of automatically selecting light-sensitive
materials, to the system of controlling transport rollers in the
light-sensitive material supply unit 16.
In the copier 10 of the present invention, the image sensor assembly 150 in
combination with the original identifying section 152 distinguishes at
least color photographic originals from color printed originals or
black-and-white originals by Discriminant Function 1 and, according to the
result of this identification, the lens unit 92 performs predetermined
adjustments of the quantity of light and color density that are
appropriate for the identified type of original, or the unit 16 supplies
the appropriate light-sensitive material.
The unit 16 has a passageway for the transport of light-sensitive materials
in a frame 28, with two magazines 30 and 32 being detachably disposed one
on the other. Rolls of light-sensitive materials 34 and 36 are
accommodated within the respective magazines and may be unwound to have
their leading edge emerge to the passageway of the unit 16. To take an
example, the light-sensitive material 34 may be a contrasty one which is
optimal for copying reflection type color printed originals, and the
light-sensitive material 36 may be a soft one which is optimal for copying
color photographic originals.
Transport rollers 42a and 42b for withdrawing the light-sensitive material
34 are disposed ahead of the magazine 30 and further ahead is a cutter 44
for cutting the light-sensitive material 34 to a predetermined length.
Transport rollers 42a and 42b receive a signal from the original
identifying section 152 and, in response to that signal, withdraw the
light-sensitive material 34 from the magazine 30.
Transport guides 48a, 48b and 48c as well as transport rollers 50 and 52
are disposed between the cutter 44 and an exposure section 46 so that the
a predetermined length of light-sensitive material 34 is guided to the
exposure section 46.
The exposure section 46 is where the exposing position 46a (exposure plane)
of the light-sensitive material 34 is defined and it comprises a glass
plate 54 fixed to face the imaging optical system of the exposing unit 18
and a plate 56 pressed against this glass plate 54.
A pair of transport rollers 58a and 58b and another pair of transport
rollers 60a and 60b are disposed upstream (in the upper part)and
downstream (in the lower part), respectively, of the exposure section 46.
Below the exposure section 46 is situated a transport guide 62 for guiding
the exposed light-sensitive material 34 downwardly in a vertical
direction. Halfway down the transport guide 62 is provided a switching
guide 64 which changes the transport of the light-sensitive material 34
(of 36) to be directed to the processing unit 20 via a branching transport
guide 66.
The magazine 32 located below the magazine 30 is equipped with a similar
mechanism to the one described above.
Transport rollers 68a and 68b and cutter 70 are provided in association
with the light-sensitive material 36. Ahead of the cutter 70 are provided
transport guides 72a and 72b as well as a transport roller 74 for
transporting the light-sensitive material 36 to a transport guide 48a.
Like transport rollers 42a and 42b, the transport rollers 68a and 68b are
so designed that they receive a signal from the original identifying
section 152 and withdraw the light-sensitive material 36 in response to
the received signal.
The exposing unit 18 is the most characteristic element of the copier 10
and comprises the following components: a platen 80 typically made of a
transparent glass plate on which a reflection type original 130 is to be
placed; a top cover 15 for holding the original in proper position on the
platen 80; an imaging optical system 82 with a movable light source that
applies the image on the platen 80 onto the light-sensitive material 34
(or 36) in the exposure section 46 by slit scanning and exposure; the
image sensor assembly 150 for measuring the reflection density of the
reflected light from the original 130 (hereinafter referred to simply as
the reflected light) during prescanning; the original identifying section
152 which, on the basis of the values of measurements with the image
sensor assembly 150, determines whether the original 130 is a color
photograph, color printed matter or a black-and-white original by
Discriminant Function 1 and which then supplies the resulting
discrimination signal to the lens unit 92 or, if the copier has a
capability of automatically selecting light-sensitive materials as shown
in FIG. 4, to the transport rollers in the light-sensitive material supply
unit 16; and a shutter 96 which acts on the optical path L of the
reflected light to connect it to either the exposure section 46 or the
image sensor 150. The imaging optical system 82 is composed of a light
source unit having a light source 84 for scanning the underside of the
platen 80 and a reflecting mirror 86, mirrors 88 and 90 which move in the
same direction as the light source unit at a speed one half the scanning
speed so as to allow the light from the light source 84 to be reflected in
a given direction, and the lens unit 92.
The lens unit 92 has a front lens group 154 and a rear lens group 156 for
allowing the reflected light from the original 130 to focus on the
exposing position 46a, a cyan filter C, a yellow filter Y and a magenta
filter M used to perform color correction on the reflected light and which
correspond to cyan, yellow and magenta colors, respectively, and plates
158 and 160 making up a movable aperture stop for correcting the quantity
of the reflected light.
In the copier 10 of the present invention, the lens unit 92 is connected to
the original identifying section 152 and, in response to a discrimination
signal from the original identifying section 152, it adjusts the quantity
and color density of the reflected light by predetermined amounts
according to the identified type of the original 130.
If the user selects the contrasty light-sensitive material 34 and if the
original 130 is identified either as color print or as a black-and-white
original, copying is effected under standard conditions that have been set
for the reproduction of contrasty image. However, if the original 130 is
identified as a color photograph, the yellow filter Y is removed and the
quantity of light is increased. If the user selects the soft
light-sensitive material 36 and if the original 130 is identified as a
color photograph, copying is effected under standard conditions that have
been set for the reproduction of soft image. However, if the original 130
is identified either as color print or as a black-and-white original, the
cyan filter C is inserted. The imaging optical system 82 in the copier 10
is so designed that the lens unit 92 moves along the optical path L for
adjusting its length, thereby enabling zooming up to a magnification of
0.5-2.0.
The shutter 96 serves to change the optical path L of the reflected light
in prescanning and exposing modes. In the prescanning mode, the shutter 96
is closed as indicated by the solid line in FIG. 4 and the optical path L
of the reflected light is connected to the image sensor assembly 150. In
the exposing mode, the shutter 96 is opened as indicated by the dashed
line and the reflected light is allowed to expose the light-sensitive
material 34 (or 36).
The image sensor assembly 150 which is used to measure the density of the
reflected light from the original 130 is of the same type as used in
constructing Discriminant Function 1 and comprises the following six
sensors having the sensitivity characteristics shown in FIG. 2:
sensors 150b.sub.1 and 150b.sub.2 having sensitivity peaks at 400 nm and
450 nm within the wavelength range of the blue (B) light;
sensors 150g.sub.1 and 150g.sub.2 having sensitivity peaks at 540 nm and
570 nm within the wavelength range of the green (G) light; and
sensors 150r.sub.1 and 150r.sub.2 having sensitivity peaks at 630 nm and
700 nm within the wavelength range of the red (R) light.
The image sensor assembly 150 also contains a condenser lens such as a
Fresnel lens for condensing the reflected light. The values of
measurements from the image sensor assembly 150 are sent to the original
identifying section 152.
The original identifying section 152 determines whether the original 130 is
a color photograph, printed matter or a black-and-white original by
Discriminant Function 1 on the basis of the values of measurements from
the image sensor assembly 150, and sends the resulting discrimination
signal to the lens unit 92 or, if the copier 10 has a capability of
automatically selecting light-sensitive materials as shown in FIG. 4, to
the light-sensitive material supply unit 16.
The construction of the original identifying section 152 is shown
schematically by a block diagram in FIG. 5. Each of the values of
measurements by the image sensor assembly 150 are sent as an output signal
to an amplifier 170 and the amplified signal is sent to an A/D converter
172 for conversion to a density signal. Two density signals obtained for
each of three primary colors are sent to a photometric data processing
unit 174 and then to RAM 176.
Subsequently, the resulting discrimination signal is sent to the lens unit
92 or, if the copier has a capability of automatically selecting
light-sensitive materials as shown in FIG. 4, to the light-sensitive
material supply unit 16. The lens unit 92 is set at predetermined
conditions for adjusting the reflected light according to the identified
type of the original, or instead a light-sensitive material appropriate
for the identified type of the original is supplied from the unit 16.
The processing unit 20 is basically composed of a processing zone 22 and a
drying zone 24. The processing zone 22 contains in it a sequence of a
developing tank 102, a bleach-fixing tank 104 and washing tanks 106 and
108 and the light-sensitive material 34 (or 36), after being developed,
bleached, fixed and rinsed with the processing solutions in these tanks,
in sent to the drying zone 24. The drying zone 24 is so constructed that
the rinsed light-sensitive material 34 (or 36) is dried and sent to a
receiving tray 110.
In the copier 10, the image sensor assembly 150 is used for identifying the
type of an original of interest but the present invention is by no means
limited to this particular case alone and as will be described
hereinafter, one way of course adopts a modification in which various
kinds of image information are obtained with the image sensor assembly 150
and the reflected light is subjected to appropriate corrections in the
lens unit 92 in accordance with the obtained image formation.
Having the basic construction described above, the image forming apparatus
of the present invention has the ability to distinguish color photographic
originals at least from color printed originals by using a discriminant
function. Black-and-white originals, whether they are printed matter or
photographs, are identified as color printed originals. An appropriate
light-sensitive material is selected according to the identified type of
the original and an image is formed on the selected light-sensitive
material.
The use of a discriminant function is not the sole method for identifying
various types of originals with black-and-white originals being judged as
color printed originals. A known method such as the one described in
Japanese Kokai 63-232681 can also be employed. In this known method, an
original of interest is judged to be a black-and-white original if it has
substantially equal spectral reflection densities for the light of three
primary colors, R, G and B, and it is judged as a color original if the
spectral reflection densities measured for the light of the three primary
colors differ so greatly that they do not agree to one another.
The originals that have been identified as black-and-white originals by the
methods described above are processed in entirely the same manner as in
the case of operating the copier shown in FIG. 4. For example, if the user
selects a contrasty light-sensitive material, it is exposed under standard
exposure conditions for contrasty materials and processed to form an
image. The associated units and their operations are the same as those
already described and need not be explained in detail. Needless to say,
standard conditions set for the processing of soft light-sensitive
materials shall be combined with a cyan (C) filter if the user selects a
soft material to form image from a black-and-white original. It should of
course be noted that color photographic originals are distinguished from
color printed originals by the methods already described or by some other
suitable methods.
An example of other methods for differentiating color printed originals
from color photographic originals is to use a two-stage discriminator
adapted from the original discriminator 178 in the original identifying
section 152 shown in FIG. 5 and which consists of, as shown in FIG. 6, a
black-and-white original identifying unit 180 which discriminates
black-and-white originals from color originals and a color original
identifying unit 182 which discriminates color printed originals at least
from color photographic originals.
The image forming apparatus of the present invention shown in FIG. 4 is
applicable to at least four kinds of silver halide photographic materials,
i.e., contrasty light-sensitive materials for black-and-white and color
printing, soft light-sensitive materials for color photography and color
slides, light-sensitive materials for color negative, and light-sensitive
materials for OHPs (overhead projectors).
Originals of the types appropriate to these light-sensitive materials and
standard exposure conditions therefor can be set by the method described
hereinafter.
The method of performing exposure with the image exposing apparatus is
intended to discriminate color photographic originals at least from color
printed originals or black-and-white originals so as to enable image
formation using a light-sensitive material that is appropriately
determined to correspond to the identified type of the original of
interest. According to this method, standard exposure conditions that are
present for image formation that involves exposing the image of a certain
type of standard original to a light-sensitive material appropriate for
said standard original are used as reference set values, and if there is a
difference in type between said standard original and the original to be
used and/or a difference between said appropriate light-sensitive material
and the light-sensitive material to be used, the set values of standard
exposure conditions are corrected by adding, to said set reference values,
those values which are predetermined for both the original and the
light-sensitive material to be used with respect to the reference standard
original and appropriate light-sensitive material, with subsequent
imagewise exposure being performed on the basis of the thus corrected
standard exposure conditions.
This method is described below more specifically. First, standard exposure
conditions such as those relating to filters (Y, M and C filters) and D
(density) adjustment are set to simulate the case where the image of a
standard original which is of the most appropriate type of original is
exposed to a commonly employed standard light-sensitive material. These
standard exposure conditions are used as reference set values for the
image exposing apparatus being considered. These reference values may be
set by the user or operator who performs manual correction on the filters
based on the results of copying tests. Alternatively, automatic setting
may be performed by having the result of a test chart copying read with a
suitable device such as the image exposing unit in a color copier.
The set reference values or standard exposure conditions and the
combination of the standard original's type and light-sensitive material
are used as a basis for setting new standard exposure conditions when the
type of original and/or the light-sensitive material is changed. This is
done by adding, to the reference set values, differences .DELTA.Y,
.DELTA.M, .DELTA.C and .DELTA.D that have been preset according to the
actually used type of original and/or light-sensitive material. On the
basis of these new standard exposure conditions, the image exposing
apparatus being considered exposes the image of the original of the new
combination to the associated light-sensitive material, thereby
reproducing a visible or latent image.
In the operation of the image exposing apparatus being considered, the
combination of the standard original's type and light-sensitive material
for obtaining the reference set values and the differences in standard
exposure conditions (.DELTA.Y, .DELTA.M, .DELTA.C and .DELTA.D) that occur
when there is a change in the original's type and/or the light-sensitive
material are preferably predetermined uniquely. This offers the following
great advantage to the operation of an image forming apparatus or a color
copier that uses the image exposing apparatus being considered: even if
the reference set values for the standard original and light-sensitive
material are reset periodically by performing actual measurements by the
setting method described above, there is no need for actual measurements
of the differences (.DELTA.Y, .DELTA.M, .DELTA.C and .DELTA.D) that result
from the variations in the settings of such reference values. The
reference set values are subject to changes for several reasons such as
the change that occurs in the image forming apparatus with time but the
differences .DELTA.Y, .DELTA.M, .DELTA.C and .DELTA.D will not vary as
greatly as these reference set values.
Therefore, even if the combination of a standard original's type and a
standard light-sensitive material is not used, the image exposing
apparatus being considered is always capable of reproducing an image
having satisfactory density, gradation, color and color balance. This is
possible without performing a copying test on every occurrence of a change
in the type of original and light-sensitive material for the purpose of
adjusting or resetting the standard exposure conditions.
A block diagram of the exposure control system in an image forming
apparatus that is used to set the standard exposure conditions described
above and to perform color correction on the basis of the so set standard
exposure conditions is shown in FIG. 7. In the image sensor assembly 150
shown in FIG. 3, two sensors are provided for each of red, green and blue
colors but for exposure control, only one sensor needs to be used for each
color. The following description of the example shown in FIG. 7 assumes
that three sensors 150r.sub.1, 150g.sub.1 and 150b.sub.2 are used to
measure red, green and blue colors, respectively.
Each of red color sensor 150r.sub.1, green color sensor 150g.sub.1 and blue
color sensor 150b.sub.2 produces an electric signal in proportion to the
quantity of incident light (exposure amount). The output signals may be
amplified as required before they are sent to associated A/D converters
184r, 184g and 184b, where they are converted to digital signals. The
resulting digital signals are subjected to signal conversion in lookup
tables 186r, 186g and 186b which have data written in for correcting the
sensitivity characteristics of sensors 150r.sub.1, 150g.sub.1 and
150b.sub.2, respectively. The lookup tables produce data for corrected
amounts of exposure. The output signals from these lookup tables are taken
into a RAM 192 via an I/O port 188 and a CPU 190.
The CPU 190 is operated in accordance with the program stored in a ROM 194
and performs sequence control on the respective parts of the system during
the calculation and automatic setting of standard exposure conditions as
appropritate for the original and light-sensitive material used, during
the setting of reference values for standard exposure conditions, and
during color copying (including prescanning). When installing the image
forming or copying apparatus to be applied, standard exposure conditions
for performing image reproduction or copying with the combination of a
standard original and a standard light-sensitive material that is
appropriate for this original are preferably stored as reference set
values in the RAM 192.
It is also preferred that when installing the apparatus, the differences
between said reference set values and the standard exposure conditions for
the case where the original and/or light-sensitive material to be used has
been changed from said standard original or light-sensitive material are
stored in the RAM 192.
A mode designating key 194 is used to select a reference value setting mode
or a copying mode. The original discriminator 178 identifies the type of
an original of interest in the manner already described. A light-sensitive
material input key 200 is used to select or manually enter the
light-sensitive material to be used. A light-sensitive material reading
unit 202 reads automatically the light-sensitive material used and may be
a reader or bar code reader which reads the mark, code or bar code on the
light-sensitive material when it is set in the copier or some other image
forming apparatus. A copy key 204 is manipulated to start the reference
value setting mode or copy mode. A cyan correction key 206, magenta
correction key 206M and a yellow correction key 206Y are manipulated to
perform desired color correction manually on the already set exposure
conditions.
When setting reference values, standard exposure conditions or corrected
exposure conditions or when correcting the standard exposure conditions
manually, CPU 190 permits motors 210C, 210M and 210Y to be driven with
drivers 208C, 208M and 208Y, respectively, so as to adjust the amount by
which color filters Y, M and C are inserted into the optical path. A
driver 208D drives a motor 210D to have the plates 158 and 160 of the
movable aperture stop move close to or apart from each other.
An illustrative method for setting standard exposure conditions with the
image forming apparatus of the present invention is described below with
reference to the case where the light-sensitive materials to be used
comprise soft light-sensitive materials which are appropriate for copying
from color photographic originals, normal light-sensitive materials
appropriate for color printed originals and OHP light-sensitive materials
appropriate for OHPS, whereas the originals to be processed comprise color
printed originals, color photographic originals, and intermediate
originals containing both printed and photographic images.
As already mentioned, the original discriminator 178 in the image forming
apparatus 10 identifies a color original of interest as a color photograph
if the value of Z of Discriminant Function 1 is positive or zero
(Z.gtoreq.0), and as printed matter if Z is negative (Z<0). If given
threshold values L.sub.P and L.sub.I are calculated from a given number of
samples, a certain original may be identified as being of an intermediate
type if L.sub.I <Z<L.sub.P.
(1) With soft light-sensitive materials, standard exposure conditions are
adjusted to provide satisfactory finish for standard photographic
originals and such standard exposure conditions are preliminarily set as
reference values in the RAM 192:
Y=Ys
M=Ms
C=Cs
A preferred design is such that if a soft light-sensitive material is
selected by manipulation of the light-sensitive material input key 200,
CPU 190 automatically calls the reference set values from RAM 192 and sets
the standard exposure conditions to said reference values (this operation
is referred to as "auto setup").
The differences between the reference set values and the standard exposure
conditions for copying a color printed original or an intermediate
original onto the soft light-sensitive material (a set of .DELTA.Y.sub.I,
.DELTA.M.sub.I, .DELTA.C.sub.I and .DELTA.D.sub.I or a set of
.DELTA.Y.sub.MS, .DELTA.M.sub.MS, .DELTA.C.sub.MS and .DELTA.D.sub.MS) are
preliminarily stored in RAM 192. When either a color printed original or
an intermediate original is selected by automatic identification with the
original discriminator 178, CPU 190 automatically sets the standard
exposure conditions as follows:
______________________________________
for color printed original
for intermediate original
______________________________________
Y = Ys + .DELTA.Y.sub.I
Y = Ys + .DELTA.Y.sub.MS
M = Ms + .DELTA.M.sub.I
M = Ms + .DELTA.M.sub.MS
C = Cs + .DELTA.C.sub.I
C = Cs + .DELTA.C.sub.MS
D = Ds + .DELTA.D.sub.I
D = Ds + .DELTA.D.sub.MS
______________________________________
The amount by which Y, M and C filters are inserted into the optical path
and the distance between plates 158 and 160 of the movable aperture stop
are automatically set to the values that satisfy these conditions.
(2) With normal light-sensitive materials, standard exposure conditions are
adjusted to provide satisfactory finish for standard printed originals and
such standard exposure conditions are preliminarily set as reference
values in the RAM 192:
Y=Y.sub.N
M=M.sub.N
C=C.sub.N
D=D.sub.N
A preferred design is such that if a normal light-sensitive material is
selected by manipulation of the light-sensitive material input key 200,
CPU 190 automatically calls the reference set values from RAM 192 and sets
the standard exposure conditions to said reference values ("auto setup"
operation).
The differences between the reference set values and the standard exposure
conditions for copying a color photographic original or an intermediate
original onto the normal light-sensitive material (a set of
.DELTA.Y.sub.P, .DELTA.M.sub.P, .DELTA.C.sub.P and .DELTA.D.sub.P or a set
of .DELTA.Y.sub.MN, .DELTA.M.sub.MN, .DELTA.C.sub.MN and .DELTA.D.sub.MN)
are preliminarily stored in RAM 192. When either a color photographic
original or an intermediate original is selected by automatic
identification with the original discriminator unit 178, CPU 190
automatically sets the standard exposure conditions as follows:
______________________________________
for color photographic
original for intermediate original
______________________________________
Y = Y.sub.N + .DELTA.Y.sub.P
Y = Y.sub.N + .DELTA.Y.sub.MN
M = M.sub.N + .DELTA.M.sub.P
M = M.sub.N + .DELTA.M.sub.MN
C = C.sub.N + .DELTA.C.sub.P
C = C.sub.N + .DELTA.C.sub.MN
D = D.sub.N + .DELTA.D.sub.P
D = D.sub.N + .DELTA.D.sub.MN
______________________________________
(3) With OHP light-sensitive material, the standard exposure conditions
that will provide satisfactory finish for standard OHP originals are set
as reference values according to similar procedures ("auto setup"
operation) to those employed in (1) and (2).
Y=Y.sub.OH
M=M.sub.OH
C=C.sub.OH
D=D.sub.OH
As in (1) and (2), the standard exposure conditions are automatically set
according to the identified type of originals:
______________________________________
for color photographic original
for color printed original
______________________________________
Y = Y.sub.OH + .DELTA.Y.sub.PO
Y = Y.sub.OH + .DELTA.Y.sub.IO
M = M.sub.OH + .DELTA.M.sub.PO
M = M.sub.OH + .DELTA.M.sub.IO
C = C.sub.OH + .DELTA.C.sub.PO
C = C.sub.OH + .DELTA.C.sub.IO
D = D.sub.OH + .DELTA.D.sub.PO
D = D.sub.OH + .DELTA.D.sub.IO
for intermediate original
Y = Y.sub.OH + .DELTA.Y.sub.MO
M = M.sub.OH + .DELTA.M.sub.MO
C = C.sub.OH + .DELTA.C.sub.MO
D = D.sub.OH + .DELTA.D.sub.MO
______________________________________
As described above, the differences from the reference set values
.DELTA.K.sub.U (K=Y, M, C, D; U=I, P, PO, IO, MS, MN, MO) are stored in
RAM 192 in the operation of the present invention. However, since the
values in parentheses are also subject to small changes, the values of
.DELTA.K.sub.U stored in RAM 192 may be occasionally corrected by actual
measurements with test charts, etc.
According to the present invention, the standard exposure conditions for
the combinations of more than one type of original with more than one
light-sensitive material are determined by adding .DELTA.K.sub.U
pre-stored in RAM 192 to the reference values that have been preset
automatically for the light-sensitive materials to be used. This method
has the advantage that even if the type of original of interest is not
appropriate for the light-sensitive material selected, standard exposure
conditions can be easily set without performing copying test and desired
image reproduction can always be ensured.
As already mentioned, reference values for soft light-sensitive materials
are so set that they are appropriate for standard photographic originals,
and those for normal light-sensitive materials and OHP light-sensitive
materials are so set that they are appropriate for standard printed
originals and standard OHP originals, respectively. Such reference values
may be set by any known method such as, for example, manual setting with
C, M, Y and D correction keys 206C, 206M, 206Y and 206D after standard
originals are subjected to repeated copying test on predetermined
light-sensitive materials. A preferred method is disclosed in commonly
assigned U.S. patent application No. 4,860,059 and comprises making a copy
on a test chart in a standard exposure condition setting mode, having the
resulting test copy read by measuring means to determine standard exposure
conditions, and using them as reference set values.
Such reference values may be set for each of the light-sensitive materials
to be used. Alternatively, with the differences in reference value between
light-sensitive materials (.DELTA.Y, .DELTA.M, .DELTA.C and .DELTA.D)
being preliminarily determined and stored in RAM 192, a copying test is
performed only with respect to a certain reference light-sensitive
material and the reference set values for it are corrected on the basis of
the test result, with the reference set values for other light-sensitive
materials being determined by adding .DELTA.Y, .DELTA.M, .DELTA.C and
.DELTA.D to the so corrected reference set values. According to another
method, initial reference set values for a plurality of light-sensitive
materials are stored in RAM 192 at an initial time, say, at the time of
system installation, and after correcting the reference set values for a
particular light-sensitive material, the differences between the initial
and corrected values are used as a basis for calculating corresponding
differences with respect to the other light-sensitive materials, thereby
setting the associated reference values.
The application of the image forming apparatus of the present invention is
by no means limited to the silver halide photographic copying machine
described above. The apparatus is also applicable to other copying
machines including those which employ various light-sensitive materials
such as pressure and light sensitive materials and photopolymers, as well
as electrophotographic copiers, and also to various types of printers.
Having described the basic construction of the image forming apparatus
according to the first aspect of the present invention, we now describe
its operation below in a specific way.
The operation starts with placing a document (original)130 on the platen 80
of the copier 10 (see FIG. 4) and closing the top cover 15. Then, copy
start button (not shown) on the copier 10 is pressed, whereupon the light
source 84 is lit to illuminate the document 130 and the light source unit
starts scanning (prescanning is initiated).
The reflected light from the document 130 falls on the mirror 86 in the
light source unit which is movable at the scanning speed. After reflection
from the mirror 86, the light is further reflected by the mirrors 88 and
90 which are movable in the same direction as the light source unit at a
speed one half the scanning speed. After passing through the lens unit 92,
the light is reflected by the shutter 96 on the position indicated by the
solid line in FIG. 4 and then reflected by the mirror 148 to be launched
into the image sensor assembly 150. In this case, the filters and variable
diaphragm stop in the lens unit 92 will not act on the optical path L and
let the light pass through unimpeded.
The reflected light launched into the image sensor assembly 150 has its
intensity measured with six sensors 150r.sub.1 -150b.sub.2 at each of the
associated wavelengths. The values of measurements in the image sensor
assembly 150 are sent to the document identifying section 152, where the
values of measurements are processed by Discriminant Function 1 to
identity the type of document 130 in such a way that color photographic
originals are differentiated at least from color printed originals or
black-and-white originals. The discrimination signal is then sent to the
lens unit 92 or, if the system has a capability of automatically selecting
the type of light-sensitive materials, to the light-sensitive material
supply unit 16.
After completion of the prescanning operation described above, the light
source unit and mirrors 88 and 90 return to the scan start position.
In the lens unit 92, predetermined correction is made for the quantity of
light and color density as appropriate for the identified type of document
according to the discrimination signal. If the system has a capability for
automatically selecting the type of light-sensitive materials, a
light-sensitive material as appropriate for the identified type of
document is selected in the light-sensitive material supply unit 16.
For example, if the document 130 is a black-and-white original with the
soft light-sensitive material 36 being selected by the user, the standard
conditions for processing soft materials are adjusted by inserting the C
filter into the optical path in the lens unit 92. If, on the other hand,
the document 130 is a color photographic original with the contrasty
light-sensitive material 34 selected by the user, the standard conditions
for processing contrasty materials are adjusted by extracting the Y filter
and opening the variable diaphragm stop by respective amounts of
approximately 6 cc and 9 cc in the lens unit 92. In the latter case, if
the contrasty light-sensitive material 34 is selected and the transport
motor (not shown) driven in the light-sensitive material supply unit 16,
transport rollers 42a and 42b feed the light-sensitive material 34 by a
predetermined length, which is then cut to the necessary length with the
cutter 44. Thereafter, the transport motor is driven again to feed the
light-sensitive material 34 to the exposure section 46 where it stops
temporarily just in front of the exposing position 46a.
When the shutter 96 rotates until it comes to the position indicated by the
dashed line in FIG. 4, it becomes possible to effect exposure by scanning.
As soon as the light source unit starts main scanning, the transport
rollers 58a, 58b, 60a and 60b in the exposure section 46 start to
transport the light-sensitive material 34 at a speed in synchronism with
the scanning by the light source 84.
During the main scanning period, the reflected light from the mirror 86
moving at the scan speed is further reflected by the mirrors 88 and 90
moving in the same direction as the mirror 86 at a speed one half the scan
speed. The reflected light is transmitted through the lens unit 92 that
has been properly adjusted in terms of color and aperture according to the
selected type of document, and the light is focused at the exposing
position 46a (exposure plane) to expose the light-sensitive material 34
being transported in synchronism with the scan speed.
As the exposure proceeds, the light-sensitive material 34 is passed between
transport rollers 58a and 58b and between transport rollers 60a and 60b
and sent further downward by passing through the transport guide 62. In
this case, the switching guide 64 does not act on the transport route of
the light-sensitive material and the material 34 being sent from the
exposure section 46 is moved down vertically through the transport guide
62. The exposed light-sensitive material 34 is thereafter sent into the
processing section 22 of the processing unit 20 but because of its
vertical downward movement, there will be no slackening of the middle
portion of the light-sensitive material 34 due to the difference in speed
between the light-sensitive material supply unit 16 and the processing
section 22.
When the exposure is completed, the shutter 96 rotates until it comes to
the position indicated by the solid line in FIG. 4, and all transport
rollers rotate in reverse direction for a short period of time while the
developed light-sensitive material 34 ascends through the transport guide
62, with part of it being fed into the transport guide 48c. The reverse
transport of the light-sensitive material 34 continues until its leading
edge comes to a position upstream of the switching guide 64.
Thereafter, each of the transport rollers is rotated in the same direction
as they were previously rotated. In this second case of rotation, the
switching guide 64 acts on the transport route of the light-sensitive
material and separates the leading edge of the light-sensitive material 34
from the transport guide 62 so that it is fed to the branching transport
guide 66. As a result, the leading edge of the light-sensitive material
passes along the branching transport guide 66 to be fed into the
processing section 22 of the processing unit 20.
The exposed light-sensitive material 34 which has been fed into the
processing section 22 is developed in the developing tank 102, bleached
and fixed in the bleach-fixing tank 104 and thoroughly rinsed in the
washing tanks 106 and 108 before it is sent to the drying zone 24. The
dried light-sensitive material 34 is fed to the receiving tray 110.
While the image forming apparatus of the present invention has basic
construction described above, it should be noted that the present
invention is by no means limited to the particular embodiments described
above and that various improvements and design modifications may be
possible without departing from the spirit and scope of the invention.
In the image forming apparatus according to the first aspect of the present
invention, the reflected light from an original of interest is measured
with two sensors for the light of each of three primary colors having
sensitivity peaks at different wavelengths within the associated
wavelength range. The resulting six values of measurements are used as
parameters for a discriminant function and the value of this function is
used as the criterion for differentiating one type of original from
another. Unlike the prior art methods of identification which need to
combine a plurality of mathematical formulas, the present invention uses
only one discriminant function and yet is capable of automatically
identifying the type of the original by discriminating color photographic
originals at least from color printed originals or black-and-white
originals in an easy and reliable way through a simple control system. The
apparatus of the present invention then forms a desired image according to
the identified type of original without giving any unwanted color shades
that may deteriorate the color balance and quality of the reproduced
image.
The image forming apparatus according to the first aspect of the present
invention has the added advantage that even an operator who is not skilled
in identifying various types of originals is capable of forming a desired
image by automatically correcting the exposure amount and colors in an
appropriate manner (i.e. matching the identified type of original) and by
selecting an appropriate light-sensitive material. As a result, even
unskilled operators are always capable of reproducing satisfactory image
that has good color balance without any undesired shades.
In the following pages, we describe the second aspect of the present
invention with reference to FIGS. 1-5 and FIGS. 8-10.
The second aspect of the present invention is also directed to
identification of the type of a color original, which is necessary when
determining the conditions for effecting image formation as appropriate
for color originals (e.g. exposure conditions such as those relating to
color filters and aperture stop) and selecting the appropriate
light-sensitive material. According to the second aspect of the present
invention, mathematical operations for identifying the type of original
are performed, with photometric values below a predetermined low level
and/or those values exceeding a predetermined high level being excluded
from the values of measurements within a photometric region including the
color original of interest. This offers the advantage of identifying the
type of the original in an accurate way even if it is an original of small
size or irregular sizes or is a thick book or a bulky material that need
copying with the top cover of the copier left open.
The method of identifying the type of original with an image forming
apparatus according to the second aspect of the present invention is
described below in detail. The reflected light from a predetermined
photometric region of the platen glass which includes a color original of
interest is measured with at least two sensors for the light of each of
three primary colors, for example, red (R), green (G) and blue (B), or for
the light of at least one primary color, where the sensors have
sensitivity peaks at different wavelengths within the wavelength regions
of the light of three primary colors or within the wavelength region of
said at least one primary color. The resulting plural, say, six, values of
photometric measurements are used as parameters of a discriminant function
and the value of this function is used as the criterion for identifying
the type of the original by discriminating at least color photographic
originals from another type of originals such as color printed originals
or black-and-white originals. In performing mathematical operations for
identification, its precision is further improved by excluding
predetermined lower levels and/or predetermined higher levels from the
values of photometric measurements with the sensors.
The following description assumes a typical case where a total of six
sensors are used, with each of three primary colors being measured with
two sensors. The term "photometric region" as used herein means the area
of the platen glass from which light is reflected to be received by the
sensors when the image information in the color original placed on the
platen glass is read or when prescanning is performed. The photometric
region may be equal to the area of the platen glass or to the size of the
documents which are the largest of all of the color documents to be
copied. Alternatively, the photometric region maybe set as a region that
matches the length of photometric scanning. It should however be noted
that in the present invention, the photometric region is preferably
determined according to the light-sensitive material on which image is to
be formed.
If the type of original is to be identified by prescanning, a single preset
region of prescanning may be used as the photometric region.
Alternatively, the photometric region may be of the same size as a
selected light-sensitive material, typically of a regular size such as B5,
B4, A4 or A3, or maybe slightly larger than these sizes.
An image forming apparatus that uses a predetermined area of the platen
glass as the photometric region suffers a certain problem if a color
original smaller than the photometric region or one of an irregular size
is set on the platen glass and held in position with a top cover the
underside of which is white. That is, when the original is scanned
photometrically by illuminating light in slit form, part of the
illumination passes through non-document area of the platen glass and is
reflected by the white underside of the top cover to be launched into the
photometric means. As a result, if copying is done in the presence of many
areas that do not contain the document, the photometric densities at small
portions of the non-document area will appear very frequently within the
range of the lowest density level. This may be represented by a histogram
in FIG. 8 which plots photometric densities at individual small portions
of the document area.
If color originals smaller than the photometric region or those which are
of irregular sizes are copied with the top cover left open, or in the case
where a certain page or pages of the thick book are copied while it is
placed face down on the platen glass with the top cover left open, the
document is not present in the photometric region or a large hollow
portion forms in the area which should inherently belong to the document
region, and the illuminating light will pass unimpeded through that area
of the platen glass which corresponds to the hollow portion, with the
consequent result that there will be little or no light that is reflected
to be incident on the photometric means, thus producing very high
photometric densities in that non-document area or the document area which
corresponds to the hollow portion. Therefore, in the case where the
photometric region contains many non-document areas of hollow portions,
the photometric densities at small portions of each non-document area or
each of the areas which correspond to the hollow portions will appear very
frequently within the range of the highest density level. This may be
represented by a histogram in FIG. 9 which plots the photometric densities
at the individual small portions of the document area.
Similar problems occur with packages or bulky materials since they are
copied without being held with the top cover or because not every part of
them can be placed in close contact with the platen glass during copying.
Hence, in order to ensure correct identification of the type of a color
original of interest, the present invention employs six sensors to obtain
photometric data which consists of six values of measurements that are
conducted at two wavelengths for the light of each of three primary
colors. Aside from the purpose of identifying the type of original, the
photometric data obtained is used to identify and calculate other factors
including image density, contrast, image areas, their densities, the
background, its density, the black background and its density. Photometry
is performed at a predetermined number of measuring points (or lines or
pixels) taken on the color original at given intervals in a certain
direction, for example, the scanning direction in the case of exposure by
scanning. If exposure is to be effected by scanning through a slit,
photometry is desirably conducted at intervals that are at least smaller
than the width of slit in the scanning direction. If the number of points
of photometry conducted in this way is written as n, the number of values
of photometric measurements is 6n (r1.sub.l, . . . r1.sub.n, r2.sub.l, . .
. r2.sub.n, g1.sub.l, . . . g1.sub.n, g2.sub.l, . . . g2.sub.n, b1.sub.l,
. . . b1.sub.n , b2.sub.l, . . . b2.sub.n) because R, G and B sensors
measure density at two wavelengths for each color.
According to the present invention, if densities r1.sub.i, r2.sub.i,
g1.sub.i, g2.sub.i, b1.sub.i and b2.sub.i measured at a certain point i
(the ith point of measurement) are within predetermined ranges and if the
differences between these densities and those densities r1.sub.j,
r2.sub.j, g1.sub.j, g2.sub.j, b1.sub.j and b2.sub.j measured at an
adjacent point j (the jth point of measurement), as expressed by
.DELTA.r1.sub.i =.vertline.r1.sub.j -r1.sub.i .vertline.
.DELTA.r2.sub.i =.vertline.r2.sub.j -r2.sub.i .vertline.
.DELTA.g1.sub.i =.vertline.g1.sub.j -g1.sub.i .vertline.
.DELTA.g2.sub.i =.vertline.g2.sub.j -g2.sub.i .vertline.
.DELTA.b1.sub.i =.vertline.b1.sub.j -b1.sub.i .vertline.
.DELTA.b2.sub.i =.vertline.b2.sub.j -b2.sub.i .vertline.
are within predetermined ranges (i.d., there are predetermined changes in
density), then the point of measurement i is judged to be within an image
area and the average density of that image area taken as a whole is used
as the corrected image area density (DM). The procedure may be described
more specifically as follows: on the basis of the color density
distributions at certain points of measurement where the values of
.DELTA.r1.sub.i, .DELTA.r2.sub.i, .DELTA.g1.sub.i, .DELTA.g2.sub.i,
.DELTA.b1.sub.i and .DELTA.b2.sub.i are within predetermined ranges,
histograms are constructed for the average density distributions of three
colors at the respective points as shown in FIGS. 8 and 9, and the density
of the image area (DM) is determined by calculating the average density
without counting in the low-density area whose density is within a
predetermined range of from D.sub.min to D.sub.min +.alpha. or the
high-density area whose density is within another predetermined range of
from D.sub.max to D.sub.max -.beta.. Thus, areas in which the change in
density is nil or very small, as well as the low-density and high-density
areas shown to be within the ranges of from D.sub.min to D.sub.min
+.alpha. and from D.sub.max to D.sub.max -.beta. in FIG. 8 to 9 will not
be regarded as part of the image region.
In identifying the image region and calculating the density of that image
region, not all of the photometric values from the six sensors described
above need be employed and instead, photometric data consisting of a given
combination of values at a single wavelength for each of R, G and B, i.e.,
r1.sub.i, g1.sub.i and b2.sub.i (i=1-n), may be used. Thus, unless
otherwise noted, the following description concerns a typical case where
the values in the red, green and blue regions are represented by r1.sub.i,
g1.sub.i and b2.sub.i (i=1-n), respectively.
In the present invention, if at least one of the values r1.sub.i, g1.sub.i
and b2.sub.i is less than a given density D.sub.min +.alpha., the point of
measurement i is taken to be within the background region and the average
density of the whole background region is used as the background density
(DB). If the background density is less than a predetermined low level,
the background area is not counted in the performance of mathematical
operations for identifying the type of original of interest.
In the present invention, if at least one of the values r1.sub.i, g1.sub.i
and b2.sub.i is greater than a given density D.sub.max -.beta., the point
of measurement i is taken to be within the black background region and the
average density of the black background region is used as the black
background density (DBB). If the black background density is greater than
a predetermined high level, the black background area is not counted in
the performance of mathematical operations for identifying the type of
original of interest.
The density level D.sub.min +.alpha. (DM.sub.L) by which to separate the
image region and the background region, and the density level D.sub.max
-.beta. (DM.sub.H) by which to separate the image region and the black
background region may be determined from the histograms of FIGS. 8 and 9
by the following procedure. The first step is to determine the values of a
minimum density D.sub.min and maximum density D.sub.max within the
photometric region. While the value of minimum density D.sub.min can be
determined by an actual photometric measurement, the density value of the
white color presented by the underside of the top cover in a copier may be
substituted. The value of maximum density D.sub.max can be determined by
an actual photometric measurement but other values can also be used, such
as a value separately set for the density of black color and the value of
photometric density for the case where neither document nor top cover is
present on the platen glass.
The values of .alpha. and .beta. are determined to lie within the
respective ranges of approximately from 1 to 20 and from 5 to 50. The
value of .alpha. may be set in such a way as to include the density of the
platen and the white underside of the top cover or the white background of
ordinary documents. The value of .beta. may be determined by the precision
of photometric measurements with sensors or by the maximum density of
ordinary reflection-type originals which normally lies between 150 and
200.
Within certain density ranges (e.g. .alpha.<20, .beta.<50), the value of
density at frequency zero or at the lowest frequency on histograms (as
indicated by D.sub.L and D.sub.H in FIGS. 8 and 9) may be detected and
counted in the image region.
In short, the values of D.sub.max, D.sub.min, .alpha. and .beta. may be set
either preliminarily or during photometric measurements with sensors.
The method of identifying the type of originals according to the second
aspect of the present invention is in no way limited and except for the
need to perform mathematical operations only on predetermined levels of
the values of photometric measurements with sensors, identification may be
conducted by the same procedures as those which are employed in the first
aspect of the invention utilizing the differences in spectral reflection
density distributions for three types of originals as depicted in FIG. 1.
Thus, there will be no need for detailed discussion in this matter.
The operation of the second aspect of the present invention is described
below more specifically with reference to the case where, as in its
already described first aspect, values of photometric measurements, r1,
r2, g1, g2, b1 and b2, which were conducted with the six sensors shown in
FIG. 2 and 3 are used as parameters of Discriminant Function 1 also
described above.
DISCRIMINANT FUNCTION 1
Z=a.sub.1 +a.sub.2 *r1+a.sub.3 *g1+a.sub.4 *b2+a.sub.5 *R+a.sub.6
*G+a.sub.7 *B where R, G and B represent r`b-r2, g2-g1, and b2-b1,
respectively. Coefficients a.sub.1 -a.sub.7 are so determined that the
ratio of S.sub.B to S.sub.W for color photographic originals and color
printed originals or black-and-white originals will assume the highest
value.
The threshold value L.sub.P for discriminating color photographic originals
from color intermediate originals and the threshold value L.sub.I for
discriminating color printed originals from color intermediate originals
can be determined through actual measurements on a number of samples. In
one example, 300 samples each of color photographic and printed originals
of size A4 were subjected to reflection density measurements under
illumination with a halogen lamp (rated at 80 V and 150 W) using the image
sensor assembly 150 shown in FIG. 5 which consisted of six sensors
150r.sub.1, 150r.sub.2, 150g.sub.1, 150g.sub.2, 150b.sub.1 and 150b.sub.2.
In the measurements with the sensors, the reflected light from each
original was shaped to a slit of the size 10 mm.times.100 mm and the
average of 70 values of reflection density measured at intervals of 3 mm
along the 210 mm side of A4 size sheet was taken as r1, r2, L.sub.P and
L.sub. I as were determined from the results of these photometric
measurements were as follows:
a.sub.1 =-14.33
a.sub.2 =-0.11
a.sub.3 =-0.37
a.sub.4 =0.45
a.sub.5 =1.19
a.sub.6 =-0.67
a.sub.7 =-0.96
L.sub.I =-5
L.sub.P =5
In this case, the values of DB (density of the background) smaller than 10
and the values of DBB (density of the black background) higher than 200
shall be excluded from the photometric data. Consequently, the color
original of interest is judged to be printed matter if Z.ltoreq.-5 in
Discriminant Function 1, and it is judged to be a photograph if
Z.gtoreq.5. The original is judged to be an intermediate one if -5<Z<5.
When the image forming apparatus according to the second aspect of the
present invention is to be used, it may be applied to a silver halide
photographic copier of the type shown in FIG. 4 in connection with the
first aspect of the invention. The original identifying section used in
this copier may be of the same type as shown in FIG. 5. Thus, there will
be no need for detailed discussion of the copier and the original
identifying section that can be used in the second aspect of the present
invention.
The following experiment was conducted with the copier 10 shown in FIG. 4
using the sensor assembly 150 shown in FIG. 3. Two types of color original
of size E were placed on the platen glass; after identifying the type of
each original by prescanning in the original identifying section shown in
FIG. 5, copying was made at a ratio of 200%. The coverage of prescanning
was equivalent to size A4.
The photometric data obtained by prescanning with the six sensors described
above was subjected to identification by Discriminant Function 1. When the
value of Z of Discriminant Function 1 was equal to or greater than 5, the
original was judged to be a photograph; when Z.ltoreq.-5, it was judged to
be printed matter; and when -5<Z<5, it was judged to be an intermediate
original.
In the experiments conducted in accordance with the present invention, all
the image data and information obtained by prescanning was used for
identification purposes when the density of the background (DB) was equal
to or greater than 10 and the density of the black background (DBB) was
equal to or less than 200, but when DB<10 or DBB>200, the image data for
the background region was excluded from the performance of mathematical
operations for identifying the type of original.
In the comparative experiments, mathematical operations for identifying the
type of original were performed using all the image data irrespective of
the value of DB and DBB.
The results of these experiments are shown in Table 2 below.
______________________________________
Experiment Experiment
Comparative of the Comparative
of the
Experiment Invention Experiment Invention
______________________________________
r2 15 36 33 42
g1 14 34 32 40
b2 13 30 28 36
r2-r1 2 7 6 8
g2-g1 0 -2 -2 -2
b2-b1 -9 -21 -17 -20
DB 1 1 2 2
Z -4.29 12.46 7.6 12.51
______________________________________
When making an enlarged copy of a small (e.g. E size) color photographic
original, prescanning is performed in such a way as to cover the
light-sensitive material on which image is to be formed (e.g., the
coverage is equivalent to size A4 at a copying ratio of 200%) but then
even the light reflected from the non-document area of the white underside
of the top cover will be launched into the sensors, thus causing erroneous
photometry. According to the present invention, the type of original is
identified after excluding those values of photometric measurements which
correspond to the level of the reflected light from the white side of the
top cover. Therefore, as is clear from Table 2, even color photographic
originals that were so small in size as to be often judged as intermediate
or color printed originals by the prior art could be correctly identified
as color photographic originals.
A similar experiment was conducted on 150 samples of color original shaving
different densities (100 of them were printed matter and 50 were
photographs) using the image forming apparatus of the present invention to
identify the type of individual samples. The results are shown in FIG. 10,
from which one can see that of the 100 samples of color printed original,
7 were identified as intermediate originals and the remainder were
correctly identified as color printed matter, with none being judged as
photographs. On the other hand, of the 50 samples of color photographic
originals, 7 were identified as intermediate originals and the remainder
were correctly identified as photographs, with none being judged as
printed matter.
As these results show, the image forming apparatus of the present invention
is capable of correctly identifying the type of originals and hence, the
image formed has satisfactory color and quality.
As described on the foregoing pages, the image forming apparatus according
to the second aspect of the present invention discriminates color
photographic originals at least from color printed originals on the basis
of the values of photometric measurements conducted on the reflected light
from a photometric region including a color original of interest.
Mathematical operations for identification purposes are performed, with
photometric values below a predetermined low level and/or those values
exceeding a predetermined high level being excluded from said values of
photometric measurements. This approach offers the advantage of precisely
discriminating color photographic originals at least from color printed
originals even if a color original smaller than the photometric region
causes the sensors to measure the reflected light from the white underside
of the top cover as if it were an image area, or even if a thick book, a
package or some other bulky material causes the sensors to perform
photometry on the large hollow portion or non-document area which is often
produced on account of copying with the top cover left open. Since precise
discrimination is achieved, the image forming apparatus of the present
invention is capable of forming image of high quality having good color
balance that is appropriate for the identified type of original. Thus, the
image forming apparatus according to the second aspect of the present
invention proves to be very effective in making enlarged copies of color
originals.
The image forming apparatus according to the second aspect of the present
invention has the added advantage that even an operator or user who has no
expertise in correctly identifying various types of color originals is
capable of automatically performing appropriate correction of exposure
amount and color according to the specific type of original no matter what
size or shape it has. Further, the operator or user is capable of
selecting the appropriate kind of light-sensitive material, thereby
ensuring the formation of a desired image with consistent quality.
An image forming apparatus according to the third aspect of the present
invention is hereunder described with reference to FIG. 4 and FIGS. 11-15.
The procedure followed by the image forming apparatus according to the
third aspect of the present invention comprises the following steps:
prescanning a color original on the platen and reading the color density
of the color original at given intervals to measure the densities of R
(red), G (green) and B (blue) colors at a number of points over the entire
region of the original, thereby obtaining a density distribution for each
color, with the area that contains a density change of a predetermined
amount being designated as an image area; constructing a density histogram
from said color density distribution; calculating the average density of
the image area, with the high-density and low-density areas within
predetermined ranges being excluded, so as to obtain the density of the
image area; obtaining a density distribution with an area, the color
density of which is below a predetermined level being designated as a
background area; determining both the background density which is the
average density of the background area and the proportion of the
background area; constructing discriminant formulas containing the image
area density, background density and the proportion of the background area
as three parameters; identifying a low-density, low-contrast original on
the basis of the constructed discriminant formulas; and performing a
predetermined density correction on the so identified low-density,
low-contrast original.
In the case of reproducing the image of a low-density, low-contrast
original such as a map on a contrasty light-sensitive material, the image
forming apparatus of the present invention adds an aperture condition of a
predetermined amount to the standard exposure conditions optimal for
exposing said contrasty light-sensitive material to obtain a latent image
on a standard original that is optimal for said light-sensitive material,
and exposure is performed with a reduced amount of exposing light. This is
effective in reproducing a low-density, low-contrast image of high quality
that is free from blocking of shadows and skipping of colors and which yet
has improved color density reproduction in the low-density areas.
If the original to be copied has a wide white background in spite of its
low density, the aperture condition is not corrected by such a method as
reduction in the amount of exposure and this enables the color density of
the original to be faithfully reproduced, thereby producing an image of
high quality that is free from fogging of the white background.
FIG. 11 shows the essential part of the image forming apparatus 220
according to the third aspect of the present invention which includes an
image exposing unit. Except for an image sensor assembly and an exposure
control system, the image exposing unit generally indicated by 230 in FIG.
11 is essentially the same as the exposing unit 18 in the silver halide
photographic copier 10 shown in FIG. 4 and like components are identified
by like numerals to eliminate the need for describing the image exposing
unit 230 in great detail. The image forming apparatus 220 has a
light-sensitive material supply unit and a light-sensitive processing unit
but their description is omitted since they can be replaced by the
light-sensitive material supply unit and processing unit 20 which are used
in the copier 10 shown in FIG. 4.
As shown in FIG. 11, the image exposing unit 230 has a transparent platen
80 on its top. When a color original 130 is placed face down on the
platen, it is held in position by means of a top cover 15 the underside of
which is white. At the left end of the platen, a standardized reflection
member 81 is provided on the underside and the reflected light from this
member is measured to adjust the white (or gray) balance.
The image exposing unit 230 has a light source unit 83 for scanning the
underside of the original 130. The light source unit 83, which is capable
of reciprocating in parallel with the platen 80, has incorporated therein
a light source 84, a slit 85a, a reflector 85b and a first mirror 86, all
of which are elongated and directed into the paper. The illumination from
the light source 84 is reflected by the original 130 and passes through
the slit 85a to form slit light, which is reflected by the first mirror 86
to be launched into a mirror unit 87.
The mirror unit 87 consists of a second elongated mirror 88 and a third
elongated mirror 90 that are capable of synchronized movement in the same
direction as the light source unit 83 at a speed one half the scan speed
and which are positioned to face each other at an angle of 45.degree. with
respect to the optical path. Because of this mirror arrangement, the unit
87 permits the light from the light source unit 83 to be reflected to
travel on the return path to be launched into a lens unit 92.
The lens unit 92 has an imaging front lens group 154 and an imaging rear
lens group 156 for focusing the image of the original 130 on the
light-sensitive material 34 (or 36) being transported in synchronism with
the light source unit 83. A yellow filter Y, a magenta filter M and a cyan
filter C are disposed between the front and rear lens groups. Behind the
rear lens group 158 is disposed an aperture stop 162 that consists of two
plates 158 and 160 which are movable in opposite direction to adjust the
quantity of light. Color filters Y, M and C are movable in a direction
perpendicular to the optical axis and by controlling the amount in which
they are inserted into the optical path, the quality of slit light is
adjusted to compensate for the color balance. In order to change the
copying ratio, the optical path length is adjusted by moving the lens unit
92 in either of the directions indicated by arrows in FIG. 11.
The light-sensitive material 34 (or 36) being transported in synchronism
with the light source unit 83 as it is held between a pair of nip rollers
58a and 58b and between another pair of nip rollers 60a and 60b is exposed
at the exposing position 46a with the light that has been adjusted in
terms of quantity, quality and focal point by means of the lens unit 92.
Needless to say, the exposure section 46 in which the exposure position
46a is located is defined by opening an elongated shutter 96 as indicated
by the solid line in FIG. 11.
When the white balance is to be corrected or when information is read from
the image of the original by prescanning, the shutter 96 is closed as
indicated by the dashed line in FIG. 11 and the image produced from the
white standardized reflection member or the image of the original is
reflected by the shutter 96 and launched into an image sensor assembly
232, thereby identifying the type of original, its color density and other
factors for determining the corrected exposure conditions.
The image sensor assembly 232 has the following components incorporated
therein: a mirror 234 by which part or all of the slit light reflected
from the shutter 96 and launched into the image sensor assembly 232 is
reflected in a horizontal direction; light condensing means 236 in the
form of a lens, Fresnel lens, condenser mirror or the like for condensing
the slit light reflected from the mirror 234; and photometric means 238
for measuring the slit light as it remains condensed by the condensing
means 236. As shown in FIG. 12, the photometric means 238 is composed of a
red (R) sensor 238a, a green (G) sensor 238b and a blue (B) sensor 238c
and performs photometry on the three primary components of the reflected
slit light. The three primary components as assumed herein are red (R),
green (G) and blue (B) but other combinations maybe selected, such as Y, M
and C.
According to the third aspect of the present invention, the color original
130 is prescanned and subjected to photometry with the image sensor
assembly 232 for identifying the type of original, its density and
contrast. Photometry is performed at a predetermined number of measuring
points (or lines or pixels) taken on the original 130 at given intervals
in the scanning direction. When exposure is to be performed by scanning
through a slit as in the image forming apparatus 220 shown in FIG. 11,
photometry is preferably conducted at intervals of d.sub.m which are at
least smaller than the width (S) of slit 85a as taken in the scanning
direction. If the number of points of photometry conducted in this way is
written as n, the number of values of photometry obtained with R, G and B
sensors 238a, 238b and 238c is 3n for the three colors.
According to the present invention, if densities R.sub.i, G.sub.i and
B.sub.i measured at a certain point i (the ith point of measurement) are
within predetermined ranges and if the differences between these densities
and those densities Rj, G.sub.j and B.sub.j measured at an adjacent point
j (the jth point of measurement), as expressed by
.DELTA.R.sub.i =.vertline.R.sub.j -R.sub.i .vertline.
.DELTA.G.sub.i =.vertline.G.sub.j -G.sub.i .vertline.
.DELTA.B.sub.i =.vertline.B.sub.j -B.sub.i .vertline.
are within predetermined ranges, then the point of measurement i is judged
to be within an image area and the average density of that image area
taken as a whole is used as the image area density (DM). The procedure may
be described more specifically as follows: on the basis of the color
density distributions at certain points of measurements where the values
of .DELTA.R.sub.i, .DELTA.G.sub.i and .DELTA.B.sub.i are within
predetermined ranges, a histogram is constructed for the average density
distributions of three colors at the respective points as shown in FIG. 13
(only the envelope of the histogram is shown), and the density of the
image area (DM) is determined by calculating the average density without
counting in the low-density area (DL) whose density is below a
predetermined low density level and the high-density area (DH) whose
density is higher than a predetermined high density level. Thus, areas in
which the change in density is nil or very small, as well as the
low-density and high-density areas indicated by DL and DH in FIG. 13 will
not be regarded as part of the image area. However, for the sake of
convenience, the average density of the original may be regarded as the
image area density (DM).
In the present invention, if at least one of R.sub.i, G.sub.i, and B.sub.i
is less than the predetermined density DL, the point of measurement i is
regarded as being located in the background area and the average density
of this background area taken as a whole is used as the background density
(DB). The proportion of the original 130 occupied by the background area
is referred to as the proportion of background area (KB).
The three parameters thus obtained, i.e., image area density (DM),
background density (DB) and the proportion of background area (KB), are
used to identify a low-density, low-contrast original by either one of the
following discriminant formulas:
DISCRIMINANT FORMULA 2
If DM.ltoreq.D11 and DB.gtoreq.DL1 and KB.ltoreq.KL1, or if DM.ltoreq.D11
and DB.ltoreq.DL2 and KB.ltoreq.KL2, then the color original 130 is
identified as a low-density, low-contrast original 1.
DISCRIMINANT FORMULA 3
If D11<DM<D12 and DB.gtoreq.DL1 and KB.gtoreq.KL1 or if D11<DM<D12 and
DB.ltoreq.DL2 and KB.ltoreq.KL2, then the color original 130 is identified
as a low-density, low-contrast original 2.
In Discriminant Formulas 2 and 3, DL1>DL2 and KL1>KL2.
The process of identifying the type of original using the image forming
apparatus 220 shown in FIG. 11 may proceed as shown in FIG. 14. Prior to
color copying, the color original is prescanned for photometry, which is
conducted for three colors, R, G, and B, with the associated color sensors
238a, 238b and 238c at predetermined points of measurements spaced by
given intervals.
Each of the outputs form sensors 238a, 238b and 238c is amplified with an
amplifier (AMP)240 and thereafter converted to a density signal in an A/D
converter 242.
The density signals for three colors, R.sub.i, G.sub.i and B.sub.i, as
obtained at each point of measurement are sent to a RAM 245 via a data
processing unit 244. After prescanning, the data processing unit 244 reads
the color density signals for the respective points of measurement from a
RAM 246 to obtain the density distribution of each color. On the basis of
the resulting color density distributions, three parameters, i.e. image
area density (DM), background density (DB) and the proportion of
background area (KB), are calculated and compared with predetermined
reference values. The result of comparison is sent to a low-density,
low-contrast original identifying section 248, where checking is made as
to whether the color original 130 is a low-density, low-contrast original.
The result of identification of low-density, low-contrast originals is sent
to an exposing condition setting unit 250, where appropriate exposure
conditions are set by reference to a ROM 252 which has stored therein the
standard exposure conditions for the combinations of various types of
originals and light-sensitive materials.
If the original of interest is identified as a low-density, low-contrast
type, appropriate exposure conditions are set by adding either one of
following values to the standard set values for exposing a contrasty
light-sensitive material such as one for making image from printed matter
(11) or and OHP light-sensitive material (12):
1. .DELTA.D.sub.L11i (i=1, 2) if the original is low-density, low-contrast
original; or
2. .DELTA.D.sub.L21i (i=1, 2) if the original is low-density, low-contrast
original 2.
Typical examples of setting exposure conditions that are appropriate for
the type of originals as identified by the present invention are given
below.
EXAMPLE 1
When the standard exposure conditions set for a normal light-sensitive
material (11) which is a contrasty light-sensitive material to be used in
forming image from printed originals consist of a yellow filter being
Y.sub.N, a magenta filter being M.sub.N, a cyan filter being C.sub.N and
an aperture being D.sub.N, the following exposure conditions (filter
conditions) are selected if the original of interest is to be used with a
normal light-sensitive material (11), is printed matter and has been
identified as low-density, low-contrast original 1:
Y=Y.sub.N
M=M.sub.N
C=C.sub.N
D=D.sub.N +.DELTA.D.sub.L11i.
EXAMPLE 2
If the original of interest is a photograph and has been identified as
low-density, low-contrast original 2, and if a normal light-sensitive
material (11) is to be used in forming image of this original, the
following exposure conditions are selected:
Y=Y.sub.N +.DELTA.Y.sub.P
M=M.sub.N +.DELTA.M.sub.P
C=C.sub.N +.DELTA.C.sub.P
D=D.sub.N +.DELTA.D.sub.P +.DELTA.D.sub.L211
where .DELTA.Y.sub.P, .DELTA.M.sub.P, .DELTA.C.sub.P and .DELTA.D.sub.P are
the amounts by which the values of Y, M, C and D of the photographic
original are corrected for the normal light-sensitive material (11).
EXAMPLE 3
When the standard exposure conditions set for an OHP light-sensitive
material (12) which is to be used in forming image from standard OHP
originals consist of Y.sub.OH, M.sub.OH, C.sub.OH and D.sub.OH, the
following exposure conditions are selected if the original of interest is
to be used with an OHP light-sensitive material (12), is an OHP original
and has been identified as low-density, low-contrast original 1:
Y=Y.sub.OH
M=M.sub.OH
C=C.sub.OH
D=D.sub.OH +.DELTA.D.sub.L112.
If the exposure conditions are set by the procedure described above,
according to these conditions the color filters Y, M and C in the lens
unit 92 shown in FIG. 11 are moved by means of a drive source such as a
motor to change the amount of their insertion into the optical path,
whereas the plates 158 and 160 making up the diaphragm stop 162 are moved
by means of a drive source such as a motor to change the amount of
exposure (see FIG. 14). In this way, the image forming apparatus 220 shown
in FIG. 11 effects appropriate image reproduction from low-density,
low-contrast originals.
Prior to image formation, the contrasty light-sensitive material 34
appropriate for use with color printed originals, or the soft
light-sensitive material 36 appropriate for use with color photographic
originals (or the OHP light-sensitive material) is fed into the exposing
section 46 from a light-sensitive material supply unit (not shown). As
already mentioned, the light-sensitive material supply unit may be of the
same construction as the light-sensitive supply unit 16 in the copier 10
shown in FIG. 4. The appropriately exposed light-sensitive material may be
subjected to wet processing in the processing unit 20 in the copier 10 if
it is a silver halide photographic material.
The image forming apparatus according to the third aspect of the present
invention has been described above with reference to the typical case
where it is a silver halide photographic copier that employs the image
exposing apparatus shown in FIG. 11. It should, however, be noted that
this is not the sole example of the present invention and the concept
described on the foregoing pages is applicable to any kind of image
forming apparatus that uses light-sensitive materials which, in addition
to silver halide photographic materials, include pressure-sensitive,
light-sensitive materials, photopolymers, thermographic light-sensitive
materials and diazo light-sensitive materials. Besides the basic
construction described above, various improvements and design
modifications are possible without departing from the spirit and scope of
the present invention.
The third aspect of the present invention may be summarized as follows: the
color density information of the image of an original of interest is read
during prescanning to obtain the density distributions of three primary
colors; three parameters are obtained by performing predetermined
mathematical operations on said color density distributions; discriminant
formulas containing the three parameters is used to determine if the
original is a low-density, low-contrast original; if a low-density,
low-contrast original such as a map is to be used to form image on a
contrasty light-sensitive material, the amount of exposure is reduced and
appropriate correction is made with respect to density, so as to achieve
improved reproduction of color density in the low-density area; in other
cases such as where the low-density original has many white background
areas, density correction is not performed by reducing the amount of
exposure or by any other methods and instead, preferential color formation
is effected in the white background, with consequent formation of a
satisfactorily reproduced image which has no problems such as fogging of
the white background.
Hence, the image as reproduced with the image forming apparatus according
to the third aspect of the present invention is of high quality in that it
features satisfactory reproduction of color density as appropriate for the
contrast of originals even if they have low density.
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